Process for the production of iron catings with a low-carbon content



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,, UNITED sures- PATENT "OFFICE.

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I I0 Drawing. Application filed August 11, 1926, Serial No. 48.628. and in Germany December 9, 19M.

It is already knowmthat by adding steel and wrought-iron scrap to a cupola furnace charge, the carbon in "cast-iron can be reduced down to acertain degree.' It is also known that hitherto it has been extremely difficult to produce castings of high quality free from blowholes, 'pipesan'd strains and also with thin walls from the material smeltad from large quantities of iron low in car- The reason for these difficulties has been supposed to be that owing to the hi gher,melt.- ing point of the part of the charge low in carbon, the charge was not thoroughly melted and the hath not uniformly mixed. Again the reduction of the carbon content did not as a rule correspond regularly with what might have been expected in View of the ratio between the the iron low in carbon and that richer in carbon. Furthermore, it was only in rare cases that a larger percentage than 20 was exceeded for the additions low in carbon (such as steel and wrought-iron) because the difficulty of producing castings capable of resisting great strains, which increases with the amount of these substances added, was well known and therefore justly feared.

It was believed, in particular, that, owing to the high melting point of the added steel and wrought-iron, a considerably greater amount of heat would be necessary than heretofore. The procedure adopted was, therefore, to burn as large a quantity of coke as possible with an increased volume of air or with an increased blast, as soon as considerable quantities of steel or cast-iron were added to the cupola furnace. By doing this, however, the result was in part the opposite of what. was aimed at. In particular the desired low amount of carbon was not obtained in the product and moreover the sulphur content was increased in accordance withthe larger amount of coke employed. Even recognized practical ex erts and research workers of high repute 0 recent times,

consider for the reason given that large additions of steel and wrought-iron scrap to the cupola. furnace are objectionable, both as regards the uniformity of the material in the finished casting and as unreliable in respect of safely attaining an accurate figure for the carbon content. They are convinced now, as they were previously, that any success in the manufacture of cast-iron low in carbon by m xlng steel or wrought-iron with pigor br ttle-iron is only possible by increasing the amount of coke used and the supply or pressure of the blast employed. For these reasons every expert at the present time considers pig-iron castings which contain on the average 2.6 to 2.8 per cent of carbon to be a reverberatory, oil or electric furnace produc v p In the latest edition of a recent work by a well-known expert, he also states in mentioning the necessity for a certain casting process of keeping the carbon content of the product within the limits of 2.5 and 3 per cent:

As will be seen, the carbon content is low. It is" hardly possible to obtain such an iron from the cupola furnace. According to Frei. the electric furnace is the best for the purpose. (Oberhofer Das technische Eisen II. Edn. 1925, Chapter Der Granguss, p. 576.)

It has also been proposed to produce pigiron with a low carbon content by running down large quantities of steel or wroughtiron in the cupola furnace, but using extraordinarily large amounts of coke and a correspondingly increased amount of air.

The present invention relates, therefore, to a new process for the production of iron castings with a lowcarbon content and therefore'of great strength. The new process is particularly suitable for the production of castings of any desired dimensions and any desired thickness of wall with a homogeneous, preponderantly per-lite texture and containing graphite in an extremely fine state of distribution, without its being necessary to take special measures to, for instance, subsequently act on the formation of the texture by troublesome heating of the moulds or to retard the speed of. cooling, as has been already advised.

The improved process, according to the present invention, consists in feeding into a cupola furnace using solid fuel and melting therein a charge whereof the iron portion consists of 50% and more of iron low in carbon (wrought-iron or steel) the remainder of the iron contained in the charge consisting of iron rich in carbon (that is, pig-iron of high total carbon and silicon content) to which total iron are added such admixtures as are usually employed in the production of grey cast-iron and a quantity of coke amounting to 9 to 13% of the total charge, and submitting said charge to a blast pressure of 400 to 800 nuns. water'gauge pressure, such pressure being varied according to whether the carbon content'in the resultant product is to be nearer 2% or 3%.

The new process proves to be, particularly economical if the iron low in carbon be used wholly or for the greater part in the form of iron in small pieces and briquetted. that is in the form of the well known shaving briquettes. I

One feature of the new process lies in the fact by using exactly the same composition of charge, the carbon content of the final product can be determined at will simply by adjusting the blast.

A cupola furnace with fore-hearth was charged with a charge which contained 60% of mild steel or iron low in carbon, the remainder of the charge consisting of 40% high silicon iron. The coke comprised 13% of the charge. The furnace was supplied all the time with blast at 450 nuns. water gauge pressure. This gave a product having a carbon content of 2.38 to 2.42 per cent over a series of successive tests. On working the furnace with a similar charge, but with ablast pressure of 800 mms, the resultant carbon content increased to 2.81 to 2.86 per cent over a series of successive tests.

The percentages of the various other constituents present in the resultant product varied only within the following narrow limits:

Silicon 2.75 -2. 99 Sulphur 0.135-0. 189 Manganese 0.92 1.16 Phosphorus 0.10 0. 12

It should be noted that the coke charge remained unaltered for all the tests, and that the condition during the different times of tests remained constant.

The above tests were taken under conditions of every-day practice. and the temperature of the furnace in all cases was in the neighbourhood of 14901500 C.

It is difficult to state a definite percentage which the coke must have, since this would depend to some extent upon the quality of the coke. which may vary at different times and places. It may be stated as a general rule, however, that the coke charge should be between 9 and 13 per cent of the total charge.

Moreover, the precise value of the most appropriate blast pressure may have to be found by experiment in the case of any particular furnace. but it is readily possible, by following the general instructions above given, to construct a graph showing the variationof the percentage carbon content. between 2 and 3 per cent in accordance with the variations of the blast pressure for any given charge, and if this is done, high grade castings having any predetermined percentage carbon content can be directly obtained as and when desired.

Thus, the new process furnishes by comparatively simple measures and without any structural alterations in the usual type of cupola furnace, the following advantages 1. A low carbon content, not usually obtained hitherto in the cupola furnace, can be obtained.

2. The carbon content can be regulated within certain limits during the smelting operation and without change in the composition of the charge and adjusted to an accurately defined value.

3. The amount of steel added may without fear be increased to 50 per cent and more, with the result that in consequence of the lower market price of steel scrap a considerable cheapening is effected in comparison with the cylinder charge hitherto usual.

4. There is a considerable improvement in the physical properties of the products and also a greater power of resistance to chemical actions.

5. The sulphur and phosphorous contents which act prejudicially on the strength of the product are kept very low.

6. Owing to the low carbon content of the cast products a practicably usable homogeneous charge is very closely approached in which, by reasons of the low carbon content, fluctuations in the silicon content varying between 1.5 and 2.5 per cent, lose the importance they possessed heretofore, as regards the texture and the physical properties of the cast-iron and also the formation of the texture for most different thickness of wall. For example, according to the new process, a carbon content of from 2.6 to 2.8 per cent can be guaranteed deliberately in the castings,

with from 2.5 to 1.5 per cent of silicon and castings can be obtained from this material which are both thick and thin in the wall without differences in texture being detectable in the different thicknesses of wall.

The invention also relates to the special construction of cupola furnaces used for carrying out the new process. The working of these furnaces is considerably facilitated, if automatic pressure reducing or pressure regulating valves be arranged at suitable points on the air pipe leading to the cupola furnace and by means of which the air can be adjusted to different ressures. By altering the adjustment of t e valves the carbon content of the cast-iron can be adjusted. The arrangement may be conveniently so devised that the adjustment of the pressure reducing or regulating valves is effected according to a scale, the units of which corre spond to definitecarbon contents.

The amount and pressure or even only the amount or only the pressure of the air passing through the furnace may be also varied or-i'egulated, for example by usingoa furmay also be employed. These may nace which is provided with means r closing it in at the top and regulating only the amount orthe ressure of escaping ases, i. e.

extracted. and arranged that they adjust the most favourable head or pressure of wind in the furnace for the purposes of the process, m'accordance with the air pressure-prevailing in front of the nozzles. These measures enable the new process to be carried out at an increased absolute air pressure in the furnace itself, but with the necessary comparatively small amounts of air or the necessary low air pressure. 7

To explain the process the 'followin results may be cited which were obtained rom experiments and conjointlytherewith by continuous working also.

A lar number of series of experiments were ma e with charges of the following composition smelted in an ordinary cupola furnace with a fore-hearth:

Snares A.

Uha/rge.50 per cent of steel and wroughtiron scrap with 0.2 per cent cai'bon.

50 per cent high silicon content pigor brittle-iron.

007w charge-12 per cent of the iron char e.

B'ast pressure-400 mm. water column.

Temperature of the bath.-Not measured.

Facility in casting and wmrkin .All kinds of machinery castings entirely free from pipes and of both thin and'thiclc walls were successfully cast and could afterwards he turned, planed, drilled and milled.

Strength of individual cast bars.

Tensile strength up to 29 kgs. per sq. mm.

Bending strength up to 74.7 kgs. per sq. mm. (untreated bar 30 mm. in diameter 600 mm. long).

Bending strength up to 60 kgs. per sq. mm. (treated bar 30 mm. in diameter 600 mm. long).

Sag up to 16.6 mm. (untreated bar 30 mm. in diameter 600 mm. long).

Sag up to 10 mm. (treated bar 36 mm. in diameter 720 mm. long).

Carbon content of the eastz'ngs.2.62.8 per cent.

Snmns B.

0harge.100 per cent steel and wroughtiron scrap with 0.2 per cent+30 E. K. castings with Si=3 per cent.

Coke 0harge.12 per cent of the charge. Blast pressw'e.-40O mm. water'column. Temperature 0 f the bat7a-1480 0. Facility in casting and working-All posmm. in diameter aible machinery castings free of pipes and ofthin and thick wall strength were successfull cast and could afterwa s be turned, plane drilled and milled.

Strength: 1. Individual cm "b Tensile strength up to 41.6 kgs. per sq. mm.

Bending strength up to 62.5 kgs. per sq. mm. (untreated ar 30 mm. in diameter 600 mm. long).

Bending strength up to 70.6 kgs. per sq. inm. )(treated bar 30 mm. in diameter 600 mm. ong

Bending strength up to 74.0 kgs. per sq. in'm. )(treated bar 15 mm. in diameter 300 mm.

ong I Sag up to 15 mm. (untreated bar 30 mm. in

diameter 600 mm. long).

Sag up to 20 mm. (treated bar 36' mm. in diameter 720 mm. long).

[1 Bars prepared from the centre of thickwalled castings.

Tensile strength: (a) up to 23.5 kgs. per sq. nun, (bar of 20 mm. in diameter prepared from lumps of 120 mm. in diameter).

(Good cylinder iron hitherto produced has this strength in individual cast bars).

(3)) up to 38.5 kgs. per sq. mm. (bar of 15 prepared from bar 42 mm. in diameter).

Bm'vwll hardmws. Ave1-age: 241-255.

per cent.

The above experiments show that, according to the invention, it is thus possible. in cupola furnaces of the usual construction, with a comparatively small quantity of coke and a comparatively feeble blast pressure to smelt up to 100 per cent steel by making use of a suitable addition of silicon and manganese to form suitable alloys and to produce castings of the higher quality of any desired dimension and thickness of walls. At the same time the castings'produced' have usually good properties as regards strength and are readily workable by turnin grinding, drilling and milling and even byliammering. The increase in the strength of the product by the simple measures taken according to this invention opens out a field for the cupolafurnace casting process which hasbeen closed to it hitherto and many other developments and is suited in particular for use in cases where hitherto the science of casting hasbeen practised merely on the lines of its previous state, for the production of walls of considerably reduced thickness. This fact in conjunction with the great simplicity and cheapness of the new process for the production of castingsof high quality constitutes the special economical importance of the invention.

It should also be mentioned that the castings produced according to the new process exhibit, in consequence of their peculiar formation of texture, a particularly high power of resistance to chemical action and are therefore eminently suited for tanksfor acids and alkalies used 1n the chemical industry. The new process also affords the possibility of producing high grade special steel alloys for special purposes, in the ordinary cupola furnace.

The action of the process may be explained as follows Since, as well known, an addition of from 10 to 15 er cent of steel or wrought-iron to pigor rittle-iron requires no increase in the coke charge, it is necessary to have the temperature required tosmelt steel and wrought-iron in the cupola furnace the same as with'the normal coke charge as it is usually :sed for the smelting of pigand brittle-iron. Starting from this consideration it was discovered that the former attempts already mentioned to compel the use of larger quantities of steel in thecupola furnace forthe production of high quality castingsfailedbecause they worked with extraordinarily large quantities of coke and as a rule also with specially high blast pressures. By this extraordinary increase in the supply of carbon used in the process, the advantage of the low carbon content of the steel and wrought-iron additions was rendered nugatory. The invention tends therefore in a way to keep the total quantity of carbon to be added in the smelting process as low as possible in any conceivable manner, yet always retaining an amount which will carbonize the steel and wrought-iron into a cast-iron which will give good castings. That the previous expe-ri ments were incapable of producing a cast product of high quality by the simple slight augmentation of the steel, or wrought-iron added with the use of larger quantities of coke, was due also (in addition to there bein too much carbon in the iron and steel to be run down) to the fact that when there are large quantities of pigand brittle-iron in the cupola furnace. upon reaching their comparatively low meltin; temperature. they run down the quickest way into the lower part of the furnace or the fore-hearth without passing through a pasty consistency. They therefore do not participate at all in the benefit of the high temperature actually prevailing in the cupola furnace and which is therefore produced su erfiuously for these large masses of pig-an brittle-iron. It must also be borne 1n mind that these comparatively large liquid masses of pig-iron must partially first also heat up the parts of the furnace through which they run, its contents and the fore-hearth to this temperature and will therefore lose heat again and partially'thcre where they flow through hotter zones act to reduce the temperature.

The case is different with the steel and wrought-iron added to the cupola furnace. At the melting tem erature of pig-iron they are not yet 1i uid, ut take up carbon even when in a re hot condition and therefore acquire a lower melting point. The castiron thus produced from the steel in the furnace has therefore a correspondingly higher temperature than the cast-iron first melted. If only comparatively small uantitics of steel be used, they scarcely su cc to effect any considerable change in the carbon content of the first smelted cast-iron. If however-and this is where the present invention comes inconsiderable quantities of steel be employed, care being taken at the same time to ensure that only a minimum of carbon is present in the furnace, the utiliza-- tion of the high furnace temperature is naturally most complete and the certainty of obtaining a low carbon content in the product correspondingly favorable.

What We claim is:

'1. A process for the production of iron castings having a low carbon content, consisting in feeding into and melting in a cupola furnace using solid fuel a charge whereof the iron portion consists of at least of iron low in carbon (wrought-iron or steel) the remainder of the iron contents contained in the char e consistin of iron rich in carbon (that is, pig-iron of igh total carbon and silicon content) to which total iron are added admixtures as are usually employed in the production of grey cast-iron and a quantity of coke amounting to between 9 and 13% of the total charge, and submitting the charge to a blast pressure of between 400 and 800 mms. water gauge pressure, such pressure being varied according to whether the total carbon content in the resultant product is to be nearer 2% or 3%.

2. In a process as specified in claim 1, charging the iron low in carbon at least partly in the formof small briquetted pieces.

In testimony whereof we have hereunto set our hands.

KARL EMMEL. HANS WALBERT. 

